1. Field of the Invention
The present invention relates to throttles for a vehicle engine, such as an internal combustion engine, and more particularly, to throttle valve control devices for controlling a throttle valve disposed within the throttle.
2. Description of the Related Art
A known throttle valve control device is disclosed in Japanese Laid-Open Patent Publication No. 3-271528 and is reproduced in FIGS. 9 to 14. As shown in FIG. 9, a throttle body 101 rotatably supports a throttle shaft 102. A throttle valve (not shown) is attached to throttle shaft 102. As shown in FIG. 11, a throttle gear 105 is mounted on the end of throttle shaft 102. Further, a relief lever 109 is pivotally mounted on throttle shaft 102 between throttle body 101 and throttle gear 105.
A clearance is provided between relief lever 109 and throttle shaft 102 so as to permit relief lever 109 to pivot. Further, clearances are also provided between relief lever 109 and throttle body 101 and between relief lever 109 and throttle gear 105. Therefore, as shown in FIGS. 11 and 13, relief lever 109 may tilt with respect to throttle shaft 102. As shown in FIG. 11, a return spring 111 is disposed around throttle body 101 and one end 111a of return spring 111 engages relief lever 109. Return spring 111 urges relief lever 109 in the valve closing direction with respect to throttle body 101. Further, a relief spring 110 is disposed within relief lever 109 and is connected to throttle gear 105. Relief spring 110 urges throttle gear 105 in the valve opening direction with respect to relief lever 109.
As shown in FIG. 9, first contact members (first contact means) 120b are provided on throttle gear 105 and relief lever 109. First contact members 120b contact each other when throttle gear 105 pivots to a predetermined pivot position in the valve opening direction. Further, second contact members (second contact means) 120a are provided on throttle body 101 and relief lever 109. Second contact members 120a contact each other when relief lever 109 pivots to a predetermined pivot position in the valve closing direction.
During operation, the position of the throttle valve within throttle body 101 is determined by the amount of torque supplied by a throttle valve controlling motor (not shown) to the throttle shaft 102, which torque acts against return spring 109. On the other hand, when the engine is not operated, the throttle valve control motor does not supply any torque to adjust the position of the throttle valve as shown in FIG. 9. In this state, return spring 111 urges throttle shaft 102 towards an initial or standby open position in which first contact members 120b contact each other at contact position 120B and second contact members 120a contact each other at contact position 120A. In the initial or standby open position, the throttle valve is slightly opened in order to permit airflow through an intake air passage in the throttle body 101. Thus, even if the throttle valve and/or throttle shaft 102 freezes in a cold environment, or adhesive materials, such as combustion products, deposit in the throttle and cause the throttle valve to be locked or stuck in the initial or standby position, airflow is still supplied to the engine. Therefore, the engine will reliably start even under these conditions.
When the throttle valve rotates in the valve opening direction from the initial or standby open position, first contact members 120b will continue contact each other at contact position 120B, as shown in FIG. 10. However, throttle gear 105 and relief lever 109 will pivot about rotational axis L of throttle shaft 102. When the throttle valve rotates from the initial or standby open position in the valve closing direction, second contact members 120a prevent rotation of relief lever 109, as shown in FIG. 12. Thus, in this state, only the throttle gear 105 will pivot about rotational axis L.
Additional description concerning Japanese Laid-Open Patent Publication No. 3-271528 can be found, for example, in the background sections of U.S. Pat. Nos. 5,735,243 and 6,164,623.
As a result of research performed by the inventors, the known throttle exhibits hysteresis around the initial or standby open position, which is believed to be caused for the following reasons. As shown in FIG. 9, contact position 120B of first contact members 120b and contact position 120A of second contact members 120a are located in separate positions that are on opposite sides of a plane P that is perpendicular to rotational axis L. Plane P includes position 120C at which the urging force of return spring 111 acts on relief lever 109. Specifically, contact position 120B of first contact members 120b is located on one side of plane P, i.e. below plane P as viewed in FIG. 9. Contact position 120A of second contact members 120a is located on the other side of plane P, i.e. above plane P as viewed in FIG. 9. As a result, relief lever 109 will tilt or pivot with respect to plane P when relief lever 109 moves from a first position (FIG. 10), in which the first contact members 120b contact each other and throttle gear 105 and relief lever 109 pivot, to a second position (FIG. 12), in which second contact members 120a prevent further rotation of relief lever 109 and only the throttle gear 105 can pivot.
Specifically, when the throttle valve rotates to the pivot position shown in FIG. 10, first contact members 120b contact each other on one side of plane P and relief lever 109 tilts downward to the right. On the other hand, when the throttle valve rotates to the pivot position shown in FIG. 12, second contact members 120a contact each other on the other side of plane P and relief lever 109 tilts downward to the left.
FIG. 14 shows a graph that relates the operating torque required by the throttle valve control motor to move the throttle valve to the various pivot positions within the working range of the known throttle described in Japanese Laid-open Patent Publication 3-271528. The abscissa represents the pivot position of the throttle valve (throttle opening position) and the ordinate represents the operating torque required by the throttle valve control motor to move the throttle valve to the respective pivot positions. As shown by FIG. 14, the operating torque is zero at the initial or standby open position B. Moreover, in the known throttle, the operating torque is also zero in a range between valve position A and valve position C, which is hysteresis with respect to the initial or standby open position. If the throttle exhibits a relatively large hysteresis, the initial or standby open position will vary during operation and thus, the amount of airflow into the throttle in the initial or standby mode will vary. However, the amount of airflow should be precisely controlled in the initial or standby open position. Thus, the known throttle exhibits a disadvantage, which is believed to be caused by the fact that the relief lever 109 pivots with respect to plane P when the throttle valve moves to the initial or standby open position B.
It is, accordingly, one object of the present teachings to provide improved throttles and more particularly, devices for controlling the position of a throttle valve disposed within the throttle.
In one aspect of the present teachings, a relief lever is preferably prevented from tilting with respect to plane P during operation, which plane P is perpendicular, or substantially perpendicular, to the rotational axis L of a throttle shaft. Therefore, the position of the throttle valve can be controlled more precisely.
In one embodiment of the present teachings, first contact members are provided on the throttle gear and the relief lever and second contact members are provided on the throttle body and the relief lever. Both the first contact members and the second contact members have contact positions that are located in plane P. In the alternative, both the first contact members and the second contact members have contact positions that are located on the same side with respect to plane P. In addition, plane P preferably includes a position in which the biasing force of a return spring acts on the relief lever. In either embodiment, the relief lever is preferably prevented from tilting with respect to plane P during operation.
Additional objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.